Electric to sonic transducer



Oct. 19, 1965 T1 q- 1. 0 A? 24' R. B. POWER ELECTRIC TO SONIC TRANSDUCER Filed Aug. 14, 1961 -I I /0 /s INVENTOR OWE BY I MM #2 gum/A ATTORNEYS United States Patent O 3,213,208 ELECTRIC T SONIC TRANSDUCER Roy B. Power, Madison, N.J., assignor to Tong-Sol Electric Inc., a corporation of Delaware Filed Aug. 14, 1961, Ser. No. 131,328 2 Claims. (Cl. 179-110) This invention relates to a transducer which transforms electric energy into sound energy. It has particular reference to a transducer which uses the property of certain ferromagnetic substances which lose their permeability when heated above a certain temperature known as the Curie point. The Curie point and its attendant phenomena are present in all ferromagnetic materials but this temperature is generally quite high, above 300 C. Recently there have been developed certain alloys which have a very low Curie temperature, about 50 C. These alloys are now available in commercial quantities. The transducers hereinafter described vary the temperature of ferromagnetic alloys above and below the Curie point, thereby varying the magnetic permeability, the magnetic flux within the material, and the magnetic force exerted upon the material.

Many forms of electric to sonic transducers have been developed and used commercially. One of these is the popular radio loud-speaker. Other forms include both high and low frequency sounding devices which can be used in various media. The transducers of the present invention have the advantage of high efficiency at low frequencies and include response characteristics which are maintained down to and including a sustained unvarying force at zero frequency.

One of the objects of this invention is to provide an improved electric to sonic transducer which avoids one or more of the disadvantages and limitations of prior art transducers.

Another object of the invention is the eificient transformation of alternating current energy into acoustic energy.

Another object of the invention is to provide a means for producing acoustic energy in an eflicient and dependable manner.

Another object of the invention is to provide a high impedance mechanical vibratory motor which can be used at low frequencies and at zero frequency.

Another object of the invention is to provide an electric vibratory motor which can be adapted to indicating means and measuring instruments.

The invention includes an electric to sonic transducer comprising a plurality of metal sheets in parallel array with resilient collapsible spacers between each of the sheets. A means is provided for producing magnetic flux in the sheets and a heating means is used for raising the temperature of the sheets to maintain them at a temperature which is close to the Curie temperature. Additional heating means is provided for varying the temperature of the sheets to vary the permeability of the sheets and thereby alter the magnetic flux.

For a better understanding of the present invention, together with other and further objects thereof, reference is made to the following description taken in connection with the accompanying drawings.

FIG. 1 is a cross sectional view of one form of the transducer using sheets separated by rubber spacers. The cross section is taken along line 1-1 of FIG. 2.

FIG. 2 is a cross sectional view of the transducer shown in FIG. 1 and is taken along line 2-2 of that figure.

FIG. 3 is a side view with some parts in section of another form of the transducer using an energizing Winding and a cone diaphragm.

FIG. 4 is a side view, with some parts in section, showing another alternate form of the transducer.

FIG. 5 is a cross sectional view of the transducer shown in FIG. 3 and is taken along line 5-5 of that figure.

Referring now to FIGS. 1 and 2, the transducer comprises a plurality of thin ferromagnetic sheets 10 arranged in parallel array and separated by resilient insulating spacers 11. The ferromagnetic sheets 10 are made of a material which has a low Curie point. That is, the magnetic characteristics undergo a considerable change when the temperature is raised above and below the Curie temperature. For most materials the permeability is high at temperatures below the Curie point and is almost zero at temperatures above the Curie point. The change in characteristic at the Curie point is usually not sudden and varies in a linear manner over a restricted range of temperatures and thereby affords a linear transfer from a series of heating and cooling cycles into sound energy.

The resilient spacers 11 between the sheets 10 may be made of ordinary rubber or, as indicated in FIGS. 1 and 2, made of sponge rubber having a great variety of collapsible air spaces in the body of the material and thereby being capable of volume compression. At one end of the array the sheets 10 are turned over to retain the rubber spacers in position. At the other end of the array the ends of the rubber spacers protrude and make contact with a plate or diaphragm 12 which may be constructed of any light material such as aluminum or plastic.

A coil 13 surrounds the array and provides heat for raising the temperature of the strips to a temperature close to the Curie point. The electric signal which is to be transformed into sound is applied to the same coil 13 (or through a parallel but separate coil) and provides heating pulses for the strips which raise them through the range of Curie temperatures and thereby alter the permeability of the strips. The coil 13 also provides lines of magnetic flux which travel through the strips, producing poles of similar polarity at the ends of the strip adjacent to the cone 12. These poles repulse each other to a certain degree when the magnetic flux is high but lower their repulsion when the temperature is raised and the magnetic flux is lowered. The alternate squeezing effect presses the ends of the rubber spacers against the diaphragm 12 and moves it to produce sound in accordance with the current variations in the coil 13.

The transducer shown in FIG. 3 is an alternate arrangement and includes a permanent magnet 14 and two pole pieces 15 and 16. The array of sheets 10 and spacers 11 is secured at one end to pole piece 15 and at the other end there exists an air gap 17. The spacers 11 in this form of transducer are preferably made of flexible rubber without air spaces since these sheets move together and do not change their position relative to each other. The free end of the array is terminated by a clamp 18 which in turn is mechanically coupled to a cone diaphragm 20 by means of a rod 21. The free end of the array may be mechanically biased by means of a helical spring 22 but this is not always necessary.

The temperature of the sheets 10 is maintained at a value within the Curie range by means of a winding 23 which surrounds the array as indicated. The temperature is best maintained by a direct current circuit which includes a source of direct current power 24, such as a battery, in series with a variable resistor 25. The terminals of this circuit are connected directly to the coil 23. The alternating signal which is to be transformed into sound is applied at terminals 26 and 27 which are connected to winding 23 in series with a large capacitor 28. The current pulses applied to winding 23 change the temperature of the sheets 1i and vary them above or below the Curie range, changing the permeability of the sheets and the magnetic flux through them and thereby vary the force across air gap 17 causing the free end of the array to vibrate and move the cone diaphragm 20.

An alternate design of a transducer is shown in FIG. 4 where one end of a permanent magnet 30 is in contact with two pole pieces 31 and 32. The ends of the pole pieces 31-32 are terminated by thin insulating spacers 33 and an array of sheets and spacers -11 is secured to these spacers 33 thereby providing a short air gap 34 between the central portion of the array and a third pole piece 35, secured to the other end of permanent magnet 30. The spacers 11 between the sheets 10 in this arrangement may be made of either flexible rubber or sponge rubber. A cone diaphragm is secured to the central portion of the array by means of a short rod 37.

The constant supply of heat necessary to maintain the ferromagnetic sheets 10 at a predetermined elevated temperature is provided by a series circuit which runs through all the sheets 10 conductively and is terminated by a direct source of potential 38 in series with an adjustable resistor 40. This circuit sends a small current through each of the sheets and raises their temperature due to the resistance loss of the material. The alternating current signal which is to be transformed into sound is applied at terminals 41 and 42 in series with a large capacitor 43. These signals, in the form of current pulses, also control the temperature of sheets 10 by means of the resistance losses in the material and because of this heating, the temperature is varied in the Curie range and the permeability is altered so that the amount of flux flowing between the array and pole pieces is sufficient to cause considerable movement of the array to vary the length of the air gap 34 and move the cone diaphragm 20.

In the above description the electric motor has been described as linked to a diaphragm for the production of sound. It will be evident that the same motor can be used for other purposes such as (1) operating an escapement for controlling the speed of rotary mechanisms, (2) operating contacts for the control of electric circuits, (3) and forming part of a temperature-sensitive control de vice.

The foregoing disclosure and drawings are merely illustrative of the princi les of this invention and are not to be interpreted in a limiting sense. The only limitations are to be determined from the scope of the appended claims.

I claim:

1. An electric to sonic transducer comprising, a plu- 5 rality of paramagnetic metal sheets in parallel array including resilient spacers between each of said sheets to maintain the sheet spacing and to form a flexible armature, said metal sheets composed of a material having a permeability which is reduced by at least percent when its temperature is raised above its Curie point, a coil of wire surrounding said sheets for producing magnetic flux in the sheets and for applying heat to the sheets to maintain their temperature near the Curie point, circuit coupling means connected to said coil for applying electrical pulses to the coil for varying the temperature of the sheets above the Curie point and thereby alter the magnetic flux within the sheets, a source of unvarying magnetic flux mounted adjacent to the sheets for producing flux in the sheets, and a diaphragm mechanically coupled to said sheets for producing mechanical vibrations and sound energy.

2. An electric to sonic transducer comprising a plurality of paramagnetic metal sheets in parallel array including resilient spacers between each of said sheets to form a flexible armature, said metal sheets composed of a material having a permeability which is reduced by at least 50 percent when its temperature is raised above its Curie point, a coil of heater Wire surrounding said sheets for applying heat to the sheets to maintain their temperature near the Curie point, circuit coupling means connected to said coil for applying electrical pulses to the coil for varying the coil temperature and the temperature of the sheets above the Curie point and thereby alter the magnetic flux within the sheets, a magnet having two poles, one end of said armature secured to one of the poles and the other end of the armature positioned adjacent to the other pole forming an air gap therebetween, a diaphragm mechanically coupled to said sheets for producing mechanical vibrations and sound energy when the other end of the armature vibrates due to the changes in magnetic flux, and a spring coupled to the armature for resiliently biasing it by acting against the magnetic force across the air gap.

Ret'erences Cited by the Examiner UNITED STATES PATENTS 271,188 1/83 Bartlett et al 179-113 396,121 1/89 Testla 310-4 2,222,425 11/40 Wehe 3l7133 2,391,313 12/45 Hindle 310-4 2,532,876 1 2/50 Asche et al. 179-11O 2,637,823 5/53 Anderson et al 179-114 OTHER REFERENCES Journal of Applied Physics, Elliot, vol. 30, N0. 11, November 1959. Pps 1774-1775.

ROBERT H. ROSE, Primary Examiner.

STEPHEN W. CAPELLI, WILLIAM C. COOPER,

Examiners. 

1. AN ELECTRIC TO SONIC TRANSDUCER COMPRISING, A PLURALITY OF PARAMAGNETIC METAL SHEETS IN PARALLEL ARRAY INCLUDING RESILIENT SPACERS BETWEEN EACH OF SAID SHEETS TO MAINTAIN THE SHEET SPACING AND TO FORM A FLEXIBLE ARMATURE, SAID METAL SHEETS COMPOSED OF A MATERIAL HAVING A PERMEABILITY WHICH IS REDUCED BY AT LEAST 50 PERCENT WHEN ITS TEMPERATURE IS RAISED ABOVE ITS CURIE POINT, A COIL OF WIRE SURROUNDING SAID SHEETS FOR PRODUCING MAGNETIC FLUX IN THE SHEETS AND FOR APPLYING HEAT TO THE SHEETS TO MAINTAIN THEIR TEMPERATURE NEAR THE CURIE POINT, CIRCUIT COUPLING MEANS CONNECTED TO SAID COIL FOR APPLYING ELECTRICAL PULSES TO THE COIL FOR VARYING THE TEMPERATURE OF THE SHEETS ABOVE THE CURIE POINT AND THEREBY ALTER THE MAGNETIC FLUX WITHIN THE SHEETS, A SOURCE OF UNVARYING MAGNETIC FLUX MOUNTED ADJACENT TO THE SHEETS FOR PRODUCING FLUX IN THE SHEETS, AND A DIAPHRAGM MECHANICALLY COUPLED TO SAID SHEETS FOR PRODUCING MECHANICAL VIBRATIONS AND SOUND ENERGY. 